1. Field of the Invention
The present invention relates to a dielectric ceramic composition having a reduction resistance, and an electric device comprising said dielectric ceramic composition in dielectric layer. Further specifically, the present invention relates to the dielectric ceramic composition and the electronic device suitable for the medium-high voltage application used at a high rated voltage (for example, 100 V or more).
2. Description of the Related Art
A multilayer ceramic capacitor as an example of the electronic device is produced, for example, by alternately stacking a ceramic green sheet comprised of a predetermined dielectric ceramic composition and an internal electrode layer having a predetermined pattern, then co-firing the green chip thus obtained as one body. Since internal electrode layers of the multilayer ceramic capacitor are formed to be one body with ceramic dielectric by firing, materials not reacting with the ceramic dielectric has to be selected. Therefore, in the related art, it has been necessary to use expensive precious metals, such as platinum and palladium, as the material composing the internal electrode layer.
In recent years, however, dielectric ceramic composition using inexpensive base metals, such as nickel and copper, have been developed and a drastic reduction of costs has been realized.
On the other hand, demands for downsizing of electronic devices have increased along with electronic circuits to have higher in density, and multilayer ceramic capacitors have rapidly become downsized with a larger capacity. Along with that, each layer of the dielectric layer of the multilayer ceramic capacitor has become thinner, thus there are demands for the dielectric ceramic composition which can maintain the reliability as a capacitor even when it is made thinner. Especially for the capacitor for the medium-high voltage application used at a high rated voltage (for example, at 100 V or more), extremely high reliability is demanded for the dielectric ceramic composition constituting the dielectric layer.
In response to this demand, for example, the Japanese Published Patent No. 3567759 discloses a dielectric ceramic compositions for the capacitor used under high frequency/high voltage comprised of; main component expressed by composition formula: ABO3+aR+bM (note that, ABO3 is a solid solution of barium titanate type, an oxide of R (a metal element such as La), and an oxide of M (a metal element such as Mn), and the subcomponent comprising a sintering aid comprised of at least one from B element and Si element. Moreover, this Japanese Published Patent No. 3567759 describes the addition of XZrO3 (note that, X is a at least one metal element selected from Ba, Sr, and Ca) as an additive component of the main component in the range of 0.35 mole or less with respect to 1 mole of solid solution of barium titanate expressed by ABO3 of the main component.
Also, the Japanese published Patent No. 3139444 discloses to calcinate the starting material of BaTiO3 and BaZrO3 so that ratio of X-ray diffraction maximum intensity of BaTiO3 becomes 5 or less with respect to ratio of X-ray diffraction maximum intensity of BaZrO3 as for the production method of the dielectric ceramic compositions which has superior reduction resistance and improved specific permittivity.
However, Japanese published Patent No. 3567759 had a problem that the voltage resistance (the breakdown voltage) was low and the lifetime characteristics (the accelerated lifetime of the insulation resistance) was insufficient, thus had less reliability. Since, such problem became prominent especially when the multilayer ceramic capacitor was downsized and the capacity was enlarged, the improvement of the voltage resistance and the lifetime characteristics (the accelerated lifetime of the insulation resistance) were demanded in order to achieve down sizing and the capacity enlargement. Note that, Japanese published Patent No. 3139444 has no description of the lifetime characteristics of the produced multilayer ceramic capacitor, and it did not solve such problem.